Patients from Fiona Stanley Hospital are sent to Fremantle and neighbouring St John of God hospitals for a specialised jaw scan because the machine required was never installed in the new tertiary facility.

The former Director General of Health, Kim Snowball, bears much of the responsibility for a $330 million cost blowout during the development of the Fiona Stanley Hospital, according to the head of a parliamentary committee.

The hospital, which was originally due to open this month, will not be fully operational until 2015.

As a result of the delay, the Education and Health Standing Committee was tasked with examining the Health Department's handling of the $2 billion hospital project.

A decision to keep the state's only prison dedicated to young male offenders just over half full has been defended by WA's Corrective Services Commissioner.

Wandoo, a minimum-security prison for men aged 18 to 24, was designed to hold 80 prisoners, but is only housing around 50.

Commissioner James McMahon has told a parliamentary committee that if the facility was made to house additional inmates, it would reduce the benefit of the prison for existing inmates who have a real chance at rehabilitation.

The outgoing under treasurer Tim Marney has revealed Treasury was only given two weeks to scrutinise a multi-billion dollar contract for the Fiona Stanley Hospital with private operator Serco before it went to Cabinet.

In July 2011 Serco was awarded the $4.3 billion dollar contract to run non-clinical support services at the hospital.

Mr Marney has told a parliamentary hearing Treasury had "extremely limited visibility" of the contract.

The State Opposition is predicting staff shortages at Fiona Stanley Hospital will result in further cost blow-outs.

It is still unclear how many full-time equivalent staff are needed to service the $2 billion hospital, but a 2012 internal report suggested the site will be short 115 staff members during the initial six-month roll-out.

The State Government has said it plans to fix the gaps by rostering staff members across different sites, during that period.

Labor's Health Spokesman Roger Cook says it is a sign the government has failed to prepare its workforce.

But the chief executive of the Fiona Stanley Hospital, David Russell-Weisz, has dismissed the concerns, saying he is confident the hospital will be fully staffed once it is commissioned.